Abstract

The role of metabolism in the generation of plasma insulin oscillations was investigated by simultaneous in vivo recordings of oxygen tension (pO₂) in the endocrine and exocrine pancreas and portal blood insulin concentrations in the anesthetized rat. At the start of the experiment, the blood glucose concentration of seven rats was 6.2 ± 0.1 mmol/l and the arterial blood pressure was 116 ± 5 mmHg. These values did not differ from those obtained at the end of the experiment. Islet pO₂ was measured by impaling superficially located islets with a miniaturized Clark electrode. The pO₂ measurements revealed slow (0.21 ± 0.03 min⁻¹) with superimposed rapid (3.1 ± 0.3 min⁻¹) oscillations. The average pO₂ was 39 ± 5 mmHg. Simultaneous recordings of pO₂ in the exocrine pancreas were significantly lower (16 ± 6 mmHg), but showed a slow and a rapid oscillatory activity with similar frequencies as seen in the endocrine pancreas. Corresponding measurements of portal insulin concentrations revealed insulin oscillations at a frequency of 0.22 ± 0.02 min⁻¹. The results are the first in vivo recordings of an oscillatory islet parameter with a frequency corresponding to that of plasma insulin oscillations; they support a primary role of metabolic oscillations in the induction of plasma insulin oscillations.